Far-red (FR) light significantly influences plant growth and development by affecting photosynthesis efficiency, photomorphogenesis, and reproductive characteristics. This study analyzed the effects of four supplemental FR light intensities (90, 60, 30, and 0 µmol/m²/s) with a peak wavelength of 35nm on the growth, yield, and physiological responses of the strawberry (Fragaria x ananassa) cultivar 'Keepsake' in a greenhouse setting under natural daylight. The study's findings indicate that elevated FR intensities (FR90 and FR60) promoted vegetative growth, as evidenced by elongated petioles, increased leaf area, and crown count. The increased intensity of FR light (FR90 and FR60) diminished the efficiency of Photosystem II (PSII) compared to FR0, indicating a potential disruption in PSII functionality, as non-regulated energy loss (PhiNO) was elevated in FR60 and FR90. Despite these physiological changes, the biomass of plants, as well as fruit diameter and weight, remained unaffected across all treatments. However, the net assimilation rate (NAR; grams of dry shoot biomass per cm² leaf area) was higher in FR60 compared to other treatments. In FR30, flowering was postponed by 51 days compared to other treatments, which correlated with the lowest fruit count, while FR90 and FR60 promoted early flowering with a higher fruit count, with FR60 plants reaching uniform flowering sooner than other FR treatments. The total sugar content (TSS) was marginally reduced in FR0. This study reveals that moderate FR intensity positively influences growth and yield, whereas low FR intensity may delay reproduction and overall yield in certain June-bearing strawberry varieties.
